1. Field of the Invention
The present invention relates to a developer to be used for electrophotography and toner jet, and to an image forming method and an image forming apparatus for visualizing an electrostatic charge image.
2. Related Background Art
A large number of methods such as an electrostatic recording method, a magnetic recording method, and a toner jet method have been conventionally known as image forming methods. For example, as described in U.S. Pat. No. 2,297,691, JP-B-S42-023910, and JP-B-S43-024748, a large number of methods have been known as electrophotographic methods. A general electrophotographic method involves: using a photoconductive substance; forming an electrical latent image on a photosensitive member by using various means; developing the latent image with toner to provide a visible image; transferring the toner onto a transfer material such as paper as required; and fixing the toner image on the transfer material by means of heat, pressure, or the like to provide a copy. The toner remaining on the photosensitive member without being transferred is cleaned by various methods, and the above steps are repeated.
In recent years, a reduced size, a reduced weight, an increased speed, and higher reliability have been strictly pursued for such copying device. For example, such copying machine has began to be used not only for paperwork for copying an original but also for: a digital printer as an output unit of a computer; copying a highly compact image such as a graphic design; and near-print where higher reliability is required (print-on-demand applications, where various kinds can be printed in a small amount, ranging from the editing of a document by means of a computer to the copying and book-binding of the document). Therefore, high definition and high image quality have been demanded. As a result, performance required for toner has become sophisticated.
For example, JP-A-H07-230182 and JP-A-H08-286421 each propose that the external addition of a magnetic powder stabilizes chargeability. According to this method, toner with stabilized chargeability and high cleaning properties can be surely obtained. However, in applications in which a high speed and improved definition and improved image quality which have been required in recent years, the method is insufficient not only because developability is insufficient but also because adhesion to a charging member occurs. In addition, JP-B-H06-093136 and JP-B-H06-093137 each propose that the addition of a charge relaxing agent to magnetic toner with a specified particle size distribution maintains high image quality while suppressing the excessive charging of the toner. Furthermore, JP-A-H08-137125 proposes that an inorganic fine particle is stuck to the surface of a toner base particle to make a potential difference between the surface of the toner base particle and the surface of the toner equal to or larger than a certain value, thereby alleviating the unevenness of charges on the surface of the toner and providing uniform charging. JP-A-2001-034006 and JP-A-2002-0207314 each propose that toner with good chargeability can be obtained by controlling the coverage of the surface of the toner with a specific inorganic fine particle and the liberation ratio of the particle from the surface of the toner. In addition, JP-A-2003-280253, JP-A-2003-280254, JP-A-H04-083258, JP-A-H04-083259, JP-A-H04-142560, JP-A-H04-269763, and JP-A-H04-350665 each propose that a magnesium oxide fine powder is added to toner to improve fluidity, whereby good chargeability can be obtained and environment dependence can be reduced.
Each of those proposals has an effect of improving chargeability. However, room is still left for each of them to be improved in applications in which a high speed and improved definition and improved image quality which have been required in recent years, i.e., applications in which even a method of use that is apt to cause toner deterioration owing to high-speed printing is required to provide image quality with high reliability and stability.